Using a media query to put sidebar images side-by-side.

Fixes #39.
Merge pull request #41 from dhermes/pan-images-on-mobile

Using a media query to put sidebar images side-by-side.
Renaming PNG to SVG before making changes.
Uses SVG instead of PNG for LaTeX images.

Also

- Removes all use of KaTeX, though this will be restored.
- Removes KaTeX css/js and fonts.
- Removes unused PNG files in content/latex_images.
- Manually sets width of SVG in <img> tags to a scaled up size.
- Sets max-width to 100% to eliminate overflow.
- Updates scripts to create and reference SVG files.

Fixes #38.